# Thanks <https://github.com/direnv/direnv/issues/73#issuecomment-152284914>
export_function()
{
  local name=$1
  local alias_dir=$PWD/.direnv/aliases
  mkdir -p "$alias_dir"
  PATH_add "$alias_dir"
  local target="$alias_dir/$name"
  if declare -f "$name" >/dev/null; then
    echo "#!$SHELL" > "$target"
    declare -f "$name" >> "$target" 2>/dev/null
    # Notice that we add shell variables to the function trigger.
    echo "$name \$*" >> "$target"
    chmod +x "$target"
  fi
}

use_guix()
{
    # Set GitHub token.
    export GUIX_GITHUB_TOKEN="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

    # Unset 'GUIX_PACKAGE_PATH'.
    export GUIX_PACKAGE_PATH=""

    # Recreate a garbage collector root.
    gcroots="$HOME/.config/guix/gcroots"
    mkdir -p "$gcroots"
    gcroot="$gcroots/guix"
    if [ -L "$gcroot" ]
    then
	rm -v "$gcroot"
    fi

    # Miscellaneous packages.
    PACKAGES_MAINTENANCE=(
	direnv
	git
	git:send-email
	git-cal
	gnupg
	guile-colorized
	guile-readline
	less
	ncurses
	openssh
	xdot
    )

    # Environment packages.
    PACKAGES=(help2man guile-sqlite3 guile-gcrypt)

    # Thanks <https://lists.gnu.org/archive/html/guix-devel/2016-09/msg00859.html>
    eval "$(guix environment --search-paths --root="$gcroot" --pure guix --ad-hoc ${PACKAGES[@]} ${PACKAGES_MAINTENANCE[@]} "$@")"

    # Predefine configure flags.
    configure()
    {
	./configure --localstatedir=/var --prefix=
    }
    export_function configure

    # Run make and optionally build something.
    build()
    {
	make -j 2
	if [ $# -gt 0 ]
	then
	    ./pre-inst-env guix build "$@"
	fi
    }
    export_function build

    # Predefine push Git command.
    push()
    {
	git push --set-upstream origin
    }
    export_function push

    clear                        # Clean up the screen.
    git-cal --author='Your Name' # Show contributions calendar.

    # Show commands help.
    echo "
build          build a package or just a project if no argument provided
configure      run ./configure with predefined parameters
push           push to upstream Git repository
"
}